docs: def addAxis(self, tag, name, minimum, maximum, default, warpMap=None):
          """ Write an axis element.
              This will be added to the <axes> element.
           """
          axisElement = ET.Element("axis")
          axisElement.attrib['name'] = name
          axisElement.attrib['tag'] = tag
          axisElement.attrib['minimum'] = str(minimum)
          axisElement.attrib['maximum'] = str(maximum)
          axisElement.attrib['default'] = str(default)
          if warpMap is not None:
              for a, b in warpMap:
                  warpPt = ET.Element("map")
                  warpPt.attrib['input'] = str(a)
                  warpPt.attrib['output'] = str(b)
                  axisElement.append(warpPt)
          self.root.findall('.axes')[0].append(axisElement)